Process for removing metallic contaminants from residual oils



Sept. 16, 1958 R. L. MENK 2,852,435

PROCESS FOR REMOVING METALLIC CONTAMINANTS FROM RESIDUAL OILS Filed Dec. 14, 1954 FIRST DEASPHALTING f ZONE Y DEASg-IALTED L 5+ I9\ i I I2 -17 l fi CYCLE (SOLVENT {14 on. I5

osifiifime F FEED ZONE STOCK SOLVENT L \FLUXED ASPHALT Robert L. Menk Inventor By Affo ney United States Patent PROCESS FOR REMOVING METALLIC CONTAMI- NANTS FROM RESIDUAL OILS Robert L. Menk, Iselin, N. J., assignor to Esso Research and Engineering Company, a corporation of Delaware Application December 14, 1954, Serial No. 475,135

Claims. (c1. 19614.46)

, This invention relates to a method of removing metallic contaminants from residual oils, and more particularly to a method for removing such contaminants by contacting the residual petroleum fraction with a wash solvent which removes the metallic contaminants without increasing the aromatic content of the residual oil.

In the past it has been proposed to treat residual petroleum fractions in various ways to remove certain metallic contaminants therefrom: Practically all residual petroleum fractions contain substantial amounts of nickel, vanadium, and iron in various forms. Such oils have been found to be undesirable feed stock. for catalytic cracking operations due to the presence of these metallic contaminants which are responsible for catalyst poisoning or contamination. Generally, it is desired to reduce the metallic content of the cracking feed stock to below one part per million. One method that has been proposed has been the useof a so-called wash oil which contains substantially no metallic components. The principle behind this operation is that a high driving force exists to transfer the metallic compounds from the residual oil to the wash oil. This transfer operation may be carried out in conjunction with a deasphalting step. Asphalt precipitated from the Wash oil descends through a deasphalting tower countercurrent to an ascending deasphalted metal containing oil. 'The descending asphalt lean in metals content scrubs the metallic components from the oil, Heavy fractions derived from catalytic cracking and lean in metallic contaminants are prime sources of wash oil for this purpose. However, these oils are characteristically high in content of aromatic compounds. Hence, any wash oil that is not precipitated in Patented Sept. 16, 1958 ice tial amount of metallic contaminants is introduced into the second deasphalting zone in conjunction with additional liquefied normally gaseous hydrocarbons and there contacts the first asphalt phase. This produces a second deasphalted phase, lean in metal contaminants, and a second asphalt phase containing the metallic contaminants. The second deasphalted phase is removed and used as a feed stock for a catalytic cracking operation while the second asphalt phase is fluxed with the deasphalted phase from the first deasphalting operation. By controlling the temperatures in the deasphalting zones so thatthe lowest temperature in the second zone is higher than the lowest temperature in the first zone, the asphalt phase produced in the first zone is of sufficiently high molecular weight to preclude the transfer of aromatics to the deasphalted oil fraction in the second deasphalting zone. In other words, by maintaining a differential between the minimum temperatures in the deasphalting zones, separation of additional aromatics from the wash oil in the second zone is prevented.

The present invention may be better understood by reference to the accompanying single figure of drawings, which is a diagrammatic representation of a typical process embodying the invention.

Turning now specifically to the drawings, a heavy cracked material such as cycle oil from a catalytic the deasphalting tower is removed in the deasphalted oil phase and contributes to an undesirable buildup of arcmatic compounds therein. In other words, removal of metallic contaminants is improved at the expense of increasing the aromaticity of the deasphalted residual oil.

It is an object of the present invention, therefore, to provide a method for removing metallic contaminants from residual petroleum fractions while substantially preventing undesirable increases in aromatics content in the treated oil.

It is a further object of the present invention to provide a process wherein residual petroleum fractions containing metallic contaminants are deasphalted and the deassubstantial amount of aromatic compounds and boiling above about 600 F. in a first deasphalting zone with a liquefied normally gaseous hydrocarbon to produce a first asphalt phase and a first deasphalted phase. The first asphalt phase is then introduced into a second deasphalt- 3, ing zone. A petroleum feed stock containing a substancracked petroleum hydrocarbon material containing a cracker or tar resulting from the thermal cracking of cycle oil and a liquefied normally gaseous hydrocarbon such as liquid propane are combined in the mixing zone 10 and transferred to the first deasp'haltingstage 11. In the first deasphalting stage 11 the temperature of the ingredients is controlled to effect the precipitation of asphaltic material of relatively high molecular weight. Normally the temperature in this stage is maintained between about l00 F. and 200 F., preferably between about F. and F. The heavy asphalt phase is removed from the first deasphalting zone through line 12,

together with dissolved hydrocarbon solvent, while the lighter deasphalted phase is removed through line 13. The heavy asphalt phase or wash oil is transferred through line 12 to a point near the top of the second deasphalting zone 14. The second deasphalting zone is preferably in the form of a vertically disposed tower through which the heavy asphalt phase drops counter current to the rising stream of lighter deasphalted residual feed stock. The residual feed stock, containing more than one part per million of metallic contaminants, is introduced through line 15 near the middle of the second deasphalting zone. at a point above that at which addi tional liquefied hydrocarbon solvent is introduced through line l6. Normally temperature conditions in the second deasphalting zone 14 are so controlled as to provide a temperature gradient between the top 17 and the bottom 18, with the temperature at'the top of the tower being higher. The temperature at the bottom of the second deasphalting tower, that is, the temperature at which the hydrocarbon solvent is introduced, must be maintained at least as high as the temperature of the first deasphalting zone in order to prevent the transfer of additional aromatic materials from the wash oil to the feed stock being deasphalted. In the second deasphalting zone 14 the residual feed stock introduced at 15 fiows downwardly against the rising stream of light hydrocarbon and is deasphalted. The deasphalted oil rises toward the top 17, and between the point of introduction 15 and the top 17 passes countercurrent to the downwardly flowing wash oil. This wash oil is essentially free of metallic contaminants so that it serves to strip these undesirable materials from the deasphalted oil while contacting it. The

deasphalted oil is then removed from the top of second deasphalting zone 14 through line 19- and may then be passed, after solvent removal, to a catalytic cracking operation, which may be carried out more successfully and with reduced danger of catalyst contamination due to the fact that metallic contaminants have been removed from the residual feed stock. The wash oil and asphalt precipitated in the lower section of the second deasphalting zone are removed together through line 20 at the bottom of the deasphalting Zone. This heavy material is then fluxed with the deasphalted phase from the first deasphalting zone in order to facilitate handling and the resulting mixture passed to a solvent recovery unit, which may be of any conventional design.

As previously stated, the temperature conditions in the second deasphalting zone must be maintained such that the minimum temperature in the second deasphalting zone is higher than the minimum temperature in the first deasphalting zone 11. The diiterential between these minimum temperatures may be as little as 5 E, but larger differentials in the order of 30-70 F. are preferred. In order to prevent undesired transfer of aromatics to the deasphalted oil, it is essential that a ditlerential between these minimum temperatures be maintained. Typically the temperature in zone 14 will be maintained in the range of about 105-250 F., and preferably in the range of about l50-230 F. In the second deasphalting zone it is preferred to employ a liquefied normally gaseous hydrocarbon, preferably or C or mixtures of these hydrocarbons, in the amount of from about 2 to 10 volumes of hydrocarbon per volume of petroleum feed stock, with a preferred range being from about 3 to about 6 volumes. In the first deasphalting zone it is preferred to use the same hydrocarbon solvent. The aromatic cracked fraction to be deasphalted is introduced in the amount of to 30% based on the volume of feed stock deasphalted in the second tower, with a range of from about 10% to about 20% being preferred. The amount of wash oil employed in the second deasphalting zone will amount to from about 2% to about based on the volume of feed stock.

The feed material for the first deasphalting zone, i. e., the material from which the wash oil is prepared, may consist of any one or more of a number of materials. A preferred material for this purpose is so-called cycle oil, which is a residual highly aromatic fraction obtained from a catalytic cracking operation and having an initial boiling point above about 600 F. and preferably above about 750 F. Heavy thermal tar obtained as a residue from the thermal cracking of cycle oil is also a suitable source of asphalt for wash oil. Since a principal object of the present invention is the minimizing of transfer of aromatics from wash oil to cracking stock, it applies to sources of wash oil high in aromatics content. Such materials are usually products of catalytic cracking operations and normally contain upwards of 50% by weight of aromatic compounds.

The following examples illustrate the operation of the process of the present invention and demonstrate the advantages to be obtained through its use, namely, the removal of metallic contaminants from a feed stock while at the same time minimizing an increase in aromaticity.

EXAMPLE I In this example a comparison is. made between the results obtained by using a catalytic tar as a wash oil (based on the volume of feed stock) as wash oil and using no wash oil are given below.

Table I Deasphnlted Deas- 7 Oil phalted Feed Catalytic Without Oil With Stock Tar Wash Oil Wash Oil Yield in Volume percent on feed 48. 4 53. 5 Specific Gravity 0.9451 0.9848 1 012 l Ccnradson Carbon, Weight percent i. 4 4. 1 19. 7 19. 1 Nickel content, parts per million 2.0 0. 6 21. 7 0. 42 Aromatic Index (percent by weight of aromatic rings). 15. l 29. 7

In operating the deasphalter using the catalytic tar as Wash 'oil, the tar was injected into the top section of the deasphalting tower. The precipitated asphalt from this tower flowed downward countercurrent to the deasphalted oil phase, and, as seen from the results set forth above, served to drastically reduce the nickel content of the oil. However, it is to be noted that this improvement is gained at the expense of a severe buildup in the aromatieity of the deasphalted oil, as indicated by an increase of from 15.1% to 29.7% by weight of aromatic rings, and also by the high specific gravity of the deasphalted oil.

EXAMPLE II A heavy catalytic tar of the same type employed as a wash solvent in Example I was deasphalted using a mixture of liquid C -C hydrocarbons (30% C in a deasphalting tower having a top temperature of F. and a bottom temperature of 151 F., to produce a light deasphalted oil and a reduced catalytic tar fraction. A ratio of hydrocarbon solvent to oil of 3.3 to 1 was employed in this deasphalting operation. Table II below gives the inspections of the catalytic tar, the deasphalted oil, and the asphalt formed. The asphalt was subsequently used as a wash solvent using the same residual petroleum fraction deasphalted according to Example I.

Table II Cycle Stock From Deas- Asphalt. Catalytic phalted Cracking 0' Yield, Volume Percent on Feed- 39. 8 60. 2 Specific Gravity at 60 F 1. 115 1. 027 1.173 Conradson Carbon, Weight Percent; 19. 1 4. 4 42. 0 Viscosity, S. S. U 11.2 9. 0 105 (275 F.) (275 F.) (300 F.) Modified Naphtha Insolubles,

Weight Percent 12. 6 0.1 30.1 Nickel Content, parts per million 0. 42 O. 2 0. 49

The second deasphalting operation was carried out using liquefied butane solvent in a ratio of six volumes of solvent per volume of feed oil. For comparison, two runs are given, one in which deasphalting was carried out using no wash solvent and another which employed 10% by volume of the asphalt precipitated according to the conditions just set forth. Table III below gives the inspections of the deasphalted oil obtained with and without wash solvent.

In carrying out the run using Wash solvent, the deasphalting temperature at the top of the tower was 221 F. and at the bottom 199 F. with the hydrocarbon solvent introduced in the middle at 203 F. In the run employing no wash oil the temperature conditions were 226 F. at the top of the tower, 201 F. at the bottom, with the residuum introduced in the middle at 201 F. The wash oil was injected near the top of the tower. Thus it will be seen that the deasphalting conditions in both runs were substantially the same with the presence or absence of asphalt as wash oil being the only difference in the runs. Comparison of the data from the two runs clearly illustrates the advantages of the process of the present invention. Not only is the nickel content substantially less, but the aromatics content of the deasphalted oil is not substantially increased as it would have been had the second deasphalting step been carried out under such conditions as to permit asphalt precipitation from the wash oil. The undersirable effects of this have been illustrated in Table I.

It is to be understood, of course, that either the first or the second deasphalting step may be carried out under conditions of constant temperature rather than in towers having a temperature gradient from top to bottom. It is necessary, however, that the minimum temperature in the second'deasphalting stage always be higher than the temperature in the first deasphalting stage. Maintenance of such a temperature difierential is necessary to avoid the solution of asphalt or aromatic material from wash oil in the second deasphalting stage with the concomitant transfer of aromatic materials to the deasphalted feed stock. In practice, however, it is generally advisable to carry out both deasphalting steps using a temperature gradient across each individual deasphalting zone.

Although there have been described in connection with the present invention specific embodiments thereof using particular materials and temperatures, it will be understood that various other equivalent materials and operating conditions may be employed without departing from the invention as defined by the following claims.

What is claimed is:

l. A method for treating a petroleum fraction feed stock containing a major portion of components boiling above 900 F. and contaminated by a substantial amount of metallic contaminants comprising the steps of treating a catalytically cracked hydrocarbon fraction containing a substantial amount of aromatic hydrocarbons in a first deasphalting zone with a liquefied normally gaseous hydrocarbon, maintaining deasphalting conditions in said zone to produce a first asphalt phase and a first deasphalted phase, withdrawing said first asphalt phase from said first deasphalting zone, introducing said first asphalt phase into a second deasphalting zone maintained at deasphalting conditions, introducing said feed stock and liquefied normally gaseous hydrocarbon into said second deasphalting zone to produce a second deasphalted phase containing less metal contaminants than said feed stock and a second asphalt phase containing metal contaminants from said feed stock, regulating the temperatures in said deasphalting zones so that the minimum temperature in said second zone is always higher than the minimum temperature in said first zone, and withdrawing said second deasphalted and second asphalt phases from said second deasphalting zone.

2. The method according to claim 1 wherein a temperature difierential of at least about 5 F. is maintained between said minimum temperatures of said deasphalting zones.

3. The method according to claim 1 wherein a temperature difierential of from about 3070 F. is maintained between said minimum temperatures of said deasphalting zones.

4. The method according to claim 1 wherein said second asphalt phase is combined with said first deasphalted phase after said second asphalt phase is withdrawn from said second deasphalting zone.

5. The method according to claim 1 wherein said deasphalting temperatures are maintained in the range of from about F. to about 250 F. g

6. The method according to claim 1 wherein said first asphalt phase introduced into said second deasphalting zone amounts to about 2% to about 15% by volume in proportion to said feed stock.

7. The method according to claim 1 wherein said cracked hydrocarbon fraction has an initial boiling point of above about 600 F.

8. The method according to claim 7 wherein said cracked hydrocarbon fraction is cycle oil.

9. A method for treating a residual petroleum fraction boiling above about 900 F. and containing more than about 1 part per million of metallic contaminants selected from the group consisting of iron, vanadium, and nickel to reduce the metallic content thereof while not substantially increasing the aromatic content thereof, comprising the steps of introducing a catalytically cracked hydrocarbon fraction containing a substantial amount of aromatic hydrocarbons into a first deasphalting zone, said deasphalting zone having a high temperature end maintained at about 170 F. and a low temperature end maintained at about F., contacting said cracked hydrocarbon fraction in said first deasphalting zone with a liquefied, normally gaseous hydrocarbon to produce a first asphalt phase and a first deasphalted phase, withdrawing said first asphalt phase from the high temperature end of said first deasphalting zone, introducing said first asphalt phase into the high temperature end of a second deasphalting zone, said second deasphalting zone having a high temperature end maintained at about 220 F. and a low temperature end maintained at about 200 F., introducing said residual petroleum fraction into said second deasphalting zone at a point intermediate said ends, introducing liquefied, normally gaseous hydrocarbon into said second deasphalting zone intermediate said ends, deasphalting said residual petroleum fraction in said second deasphalting zone to produce a second deasphalted phase containing less metallic contaminants than said feed stock and having substantially the same aromatic content as said residual petroleum fraction, and a second asphalt phase containing metallic contaminants from said feed stock, withdrawing said second asphalt phase from the low temperature end of said second deasphalting zone and Withdrawing said second deasphalted phase from the high temperature end thereof, and subsequently fluxing said second asphalt phase with said first deasphalted phase.

10. The method according to claim 9 wherein the amount of cracked hydrocarbon introduced into said first deasphalting zone amounts to from about 5% to about 30% by volume of the residual petroleum fraction introduced into said second deasphalting zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,079,886 Voorhies May 11, 1937 2,500,757 Kiersted Mar. 14, 1950 2,600,389 Benedict June 17, 1952 2,700,637 Knox Jan. 25, 1955 

1. A METHOD FOR TREATING A PETROLEUM FRACTION FEED STOCK CONTAINING A MAJOR PORTION OF COMPONENTS BOILING ABOVE 900*F. AND CONTAMINATED BY A SUBSTANTIAL AMOUNT OF METALLIC CONTAMINANTS COMPRISING THE STEPS OF TREATING A CATALYTICALLY CRACKED HYDROCARBON FRACTION CONTAINING A SUBSTANTIAL AMOUNT OF AROMATIC HYDROCARBONS IN A FIRST DEASPHALTING ZONE WITH A LIQUEFIED NORMALLY GASEOUS HYDROCARBON, MAINTAINING DEASPHALTING CONDITIONS IN SAID ZONE TO PRODUCE A FIRST ASPHALT PHASE AND A FIRST DEASPHALTED PHASE, WITHDRAWING SAID FIRST ASPHALT PHASE FROM SAID FIRST DEASPHALTING ZONE, INTRODUCING SAID FIRST ASPHALT PHASE INTO A SECOND DEASPHALTING ZONE MAINTAINED AT DEASPHALTING CONDITIONS, INTRODUCING SAID FEED STOCK AND LIQUEFIED NORMALLY GASEOUS HYDROCARBON INTO SAID SECOND DEASPHALTING ZONE TO PRODUCE A SECOND DEASPHALTED PHASE CONTAININ LESS METAL CONTAMINANTS THAN SAID FEED STOCK AND A SECOND ASPHALT PHASE CONTAINING METAL CONTAMINANTS FROM SAID FEED STOCK, REGULATING THE TEMPERATURES IN SAID DEASPHALTING ZONES SO THAT THE MINIUM TEMPERATURE IN SAID SECOND ZONE IS ALWAYS HIGHER THAN THE MINIMUM TEMPERATURE IN SAID FIRST ZONE, AND WITHDRAWING SAID SECOND DEASPHALTED AND SECOND ASPHALT PHASES FROM SAID SECOND DEASPHALTING ZONE. 